Question re snapshot database and source DB

We have a few snapshot databases (oakcli create snapshotdb), and I always assumed that if the source database was ever removed then the snapshot database would be "orphaned" and therefore encounter problems.   But recently we needed to remove and recreate a source database, and to our surprise the snapshot database that was previously created from that source database still remained up and could be queried.   Can anybody explain how that is so?   The snapshot was recreated from the new source less than 24 hours later, so we didn't have a lot of time to thoroughly test the "orphaned" snapshot. 

We have a test database that we refresh (re-duplicate from production) once a month, and I've been hesitant to create it as snapshot because occasionally the source needs to be recreated, and I was afraid if that happened it would invalidate the snapshot.   But now I'm wondering if we should clone that test database as a snapshot instead.    Does anybody else have experience creating a snapshot and then needing to delete the source database?